title: Lifting della repression of Arabidopsis seed germination by nonproteolytic gibberellin signaling.
abstract: DELLA repression of Arabidopsis (Arabidopsis thaliana) seed germination can be lifted either through DELLA proteolysis by the ubiquitin-proteasome pathway or through proteolysis-independent gibberellin (GA) hormone signaling. GA binding to the GIBBERELLIN-INSENSITIVE DWARF1 (GID1) GA receptors stimulates GID1-GA-DELLA complex formation, which in turn triggers DELLA protein ubiquitination and proteolysis via the SCF(SLY1) E3 ubiquitin ligase and 26S proteasome. Although DELLA cannot be destroyed in the sleepy1-2 (sly1-2) F-box mutant, long dry after-ripening and GID1 overexpression can relieve the strong sly1-2 seed dormancy phenotype. It appears that sly1-2 seed dormancy results from abscisic acid (ABA) signaling downstream of DELLA, since dormant sly1-2 seeds accumulate high levels of ABA hormone and loss of ABA sensitivity rescues sly1-2 seed germination. DELLA positively regulates the expression of XERICO, an inducer of ABA biosynthesis. GID1b overexpression rescues sly1-2 germination through proteolysis-independent DELLA down-regulation associated with increased expression of GA-inducible genes and decreased ABA accumulation, apparently as a result of decreased XERICO messenger RNA levels. Higher levels of GID1 overexpression are associated with more efficient sly1 germination and increased GID1-GA-DELLA complex formation, suggesting that GID1 down-regulates DELLA through protein binding. After-ripening results in increased GA accumulation and GID1a-dependent GA signaling, suggesting that after-ripening triggers GA-stimulated GID1-GA-DELLA protein complex formation, which in turn blocks DELLA transcriptional activation of the XERICO inhibitor of seed germination.
authors.affiliation: Department of Crop and Soil Science, Washington State University, Pullman, Washington 99164-6420, USA.
authors.forename: Tohru
authors.initials: T
authors.lastname: Ariizumi
authors.forename: Amber L
authors.initials: AL
authors.lastname: Hauvermale
authors.forename: Sven K
authors.initials: SK
authors.lastname: Nelson
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hanada
authors.forename: Shinjiro
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Camille M
authors.initials: CM
authors.lastname: Steber
mesh_terms: D000040:Abscisic Acid / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D035264:Flowers / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000502:physiology*; D005875:Gibberellins / Q000378:metabolism*; D009154:Mutation; D057445:Plant Dormancy / Q000235:genetics; D018520:Plant Shoots / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; C109555:GAI protein, Arabidopsis; C512225:GID1a protein, Arabidopsis; D005875:Gibberellins; D011956:Receptors, Cell Surface; C513943:XERICO protein, Arabidopsis; D000040:Abscisic Acid